Dava Sobel

Longitude

The true story of a lone genius who solved the greatest scientific problem of his time

Those of us who are not seafarers or naval historians may not be aware of
how difficult and dangerous it was to navigate in the days before a ship's
longitude could be known precisely. In 1707 four out of five warships
foundered on the Scilly Isles, off the south-west tip of England, as the
result of an error of longitude; two thousand men were drowned and only two
survived, one of whom was the Admiral—and he was murdered by a
beachcombing woman for the sake of his emerald ring. Disasters of this sort
caused Parliament to offer a twenty-thousand-pound reward for the invention
of a means of keeping time accurately at sea, for knowledge of the time was
the key to determining longitude. The problem was ultimately solved by John
Harrison, a self-taught Yorkshire clockmaker, but not without a prolonged
battle not only with the technicalities of clock-making but also with
prejudice in high quarters.

The main rival system that Harrison had to compete against was not
mechanical but astronomical. It depended on observing the motions of the
moon, using the recently invented sextant. This did work, but was
extremely difficult to do in practice, owing to the problem of making
accurate observations from a moving deck and also the complicated
mathematical calculations required. Harrison's clock, in contrast, was
simple to use, but this didn't please those who had invested effort and
prestige in the astronomical method. The superiority of the clock could not
ultimately be denied, but Harrison did not receive the full credit due to
him until he was in his seventies, and even then only with the assistance
of the King himself. Moreover, although he was paid most of the money he
was entitled to, it was in the form of a bounty from Parliament, not the
prize itself, which was never finally awarded to anyone.

The story has been well told by Dava Sobell in this short book. She
explains the intrigues that went on and also gives a clear account of the
nature of the navigational problem that had to be solved. However, there is
not a great deal of information about the mechanism of the clocks
themselves; I should have liked to have more details of their construction,
perhaps with some diagrams, though no doubt this would have made the book a
great deal longer.